1. Field of the Invention
This invention relates to a control device in an optical disc player that records and plays back (reproduces) information on and from an optical disc serving as a data recording medium.
2. Description of the Related Art
Optical discs are used as media for recording audio signals and video signals. The optical discs form rows of pits on the disc surface as tracks to record information. When retrieving (playing back) the recorded information from the optical disc, the pit rows are detected by an optical pickup and converted into electrical signals. The electric signals are then used as the audio signals and video signals to reproduce the recorded sound and image.
During the reproduction of the recorded information, the optical disc is rotated at a high speed by, for example, a spindle motor, and the rotating speed of the spindle motor is accurately controlled by a rotation rate control circuit. Also, the optical pickup is controlled by a focusing servo and a tracking servo in order to accurately detect pit rows.
In this specification, spindle motor rotation rate control is referred to as “spindle control”, and various control servo operations for the optical pickup are referred to as “repetitive control”. The repetitive control is one method of achieving high-precision control processing in ordinary control systems. The repetitive control method takes advantage of a fact that when the input signals to the control system are repetitions of substantially the same waveform, the input signals are a repeated waveform. In the repetitive control method, therefore, every time the repetition of the input signal occurs, the preceding control deviation is reflected in the control at that instant. When such repetitive control is applied to a focusing servo, tracking servo or a similar operation during optical disc recording and reproduction, errors which occur in synchronization with the rotation period of the optical disc and arise from optical disc eccentricity and runout can be eliminated.
FIG. 1 of the attached drawings illustrates a block diagram of the configuration of a control circuit to perform the control described above in a conventional optical disc player.
In the figure, an optical disc 10 is a recording medium, with various information recorded in pit rows provided on the surface of the optical disc. A spindle motor 11 is a motor to rotate the optical disc 10 at high speed during information reproduction. The rotation rate can be freely controlled by means of a rotation rate control command. A spindle motor rotation rate detector 12 includes, for example, a rotary encoder and an associated processing circuit, and generates a spindle motor rotation rate detection pulse (hereafter called simply an “FG (frequency generator) pulse”) upon each rotation of the spindle motor 11 through a prescribed angle. The processing circuit processes a detection signal resulting from the rotary encoder.
A rotation frequency detector 13 is a circuit to detect the rotation frequency of the spindle motor 11, based on the FG pulses supplied by the spindle motor rotation rate detector 12. A spindle motor controller 14 is a circuit which generates a rotation control command so as to rotate the spindle motor 11 at a desired speed, based on the frequency detected by the rotation frequency detector 13. A spindle motor driver 15 is a motor driving circuit that includes, for example, a power transistor, power FET or the like, and controls the spindle motor 11 to rotate at a rotation rate based on the rotation rate control command from the spindle motor controller 14.
A PLL controller 16 is a signal frequency-multiplier circuit utilizing a PLL (phase-locked loop) circuit. In the PLL controller, the FG pulse supplied from the spindle motor rotation rate detector 12 is multiplied by a prescribed value, to generate a sampling pulse required by a repetitive control unit 17, described below. The repetitive control unit 17 receives various error input signals supplied from an optical pickup driver (not shown), such as tracking error signals and focusing error signals, in synchronization with the sampling pulse, and executes the prescribed repetitive control. The execution of the repetitive control is accompanied by the output from the repetitive control unit 17 of various control signals to servomechanisms and actuator mechanisms of the optical pickup driver. By this means, focusing servo, tracking servo, and other servo control of the optical pickup is performed.
As described above, in a conventional optical disc player the circuit components which handle the spindle control and repetitive control are configured independently, thereby creating a problem of an increased number of component parts in the optical disc player. The PLL controller 16 is normally an analog circuit including a phase comparator, loop filter, and VCO (voltage-controlled oscillator), as taught in Japanese Patent Kokai (Laid-open publication) No. 9-35289. Consequently it has been difficult to incorporate the circuitry in an LSI device, and this difficulty has impeded efforts to reduce the size and the power consumption of an optical disc player itself.